Tone arm



R. S. JOHN Feb. 20, 1951 TONE ARM 2 Sheets-Sheet 1 Filed Jan. 23, 1945fiver? an [3 0567713 R. s. JOHN 2,542,534

TONE ARM 2 Sheets-Sheet 2 Feb. 20, 1951 Filed Jan. 23,

42587713 Jazz,

Patented Feb. 20, 1951 UNITED STATES PATENT oFFice TONE ARM4 1 Claim;(01. 2i 4"-23') This invention relates to atone arm andparpressureraridto provide a heavy-baseelemeiit on" ticularlyjto astonearm assembly ina recorde which the supported "end of the arm"ispivoted;']- playing device in which theprincipal function of to-produceahigh momentofinertia; witha light thetone arm istoprovide a movableholder to weight-arm; .tha-t' can-rotatehorizontallywith carry thetranslating means andneedle across=5 thearrn-andprovide'amextra'amountof horizon the record.

talstabilityfor the cartridgef I a I Among the objects-ofthe'inventionis to-pro- Further-objects, advantagesand capabilities?vide a movable-extension arm which will efiect inherently :possesse'd'by my invention will later stable support-for'an .apparatuscapableof--trans+ more fully becomeapparent. I I latinga forced vibration intoa fluctuating elec l My' invention further resides-in thecombinaif triocurrent; further to provide -atone 'ar'm in tion, construction andarrangementfof'parts" ilwhich 7 the cartridge housing-a thetranslatinglustrated--in 'the accompanying drawin s; and" means-disset'at'anangle to-the arm to allow the .whileI have 'shown 'therein'preferred eI'r'ibodi-" needle to cross the record approXimate1yon aments I wish-it understoodthat-"the:same"are radius and the cartridge beas nearly tangent to 16 susceptible "of modifica'tion and change-withouteach" record'groove as possible; still fur-ther to departing from thespirit of my invention. provide a tone arm that 'wi'll'function with alow- In thedrawings: I I needle pressure and supply sufiicient momentumFigfil is a side "edge elevation of'fa tone armyand inertia to-allow theneedle'to reproduce a embodying my inventionand showing -a record broadrange offrequencies :with' high-fidelityy-i-ZO tableandrecord'in-dotted'lines-E II I I yet further; the-feature of providing-anovel' tone- Fig-f2 is :a top' plm' VieWbf-the'tme arm as arm in whichthe center: of gravitysof the car sembly-bf II II I I I tridge and-armis near'the needle-point; thefur=-- Fig'. 3 is a vertical' transverseIse'otion onithe ther feature of providing ato'ne' arm-in 'which' line3'"3"of-Fig. 2 looking in the direction of the the arm and cartridge.are'free torotate in ver' arrowsi I I ticalplanesl andhorizontalflplanea but no fur Fig; 4 isavieW-similar to that of-Figf lbut thermotion; alsostoprovide a tone arm-'compris"- Showing-a modifiedform of 'my inventi V ing a framework or arms madebf thin wall tub g'iS'a toprlan 'V W he o'n afhi as ing and so constructed and arranged'as:to 'pre sembly shownin Fig.4;" I I I vent any wobbling of'thecartridge; further 'the Figx 6 is a vertical transverse'section "onthefl provision of a movable vibration damper that can lin'e- 6+6 ofFi"g;- 5 "looking inthe direction of beselectively fastened tonne of the-arm -mem"- the'arrowsi" I t any point Where-a vibration. p Referring more-in detail to the drawings my: occur-at-low frequencies,andto-preventorm preferred "form" of the invention is shown inf Figs.--'-1-3'-'and comprises a pair of spacd apart angularly arrangedarm-elements I and- 2 as; shown 'in Fig. 2 and rigidly 'con-r'iecte'dtogether at "their forwardends by a eonnectingarins and at their rearends by a curved U-shaped mem ber"4. Therear ends of the arm elementsare I rigidly-securd to' the U-shapedmi riber 4 byff any-suitable meanstofrigidly' 'hold thes'e parts also to place'the connecting wiresins'ide'of the tubing to shield themrfrom any outside-magnetic orelectrostatic fields; to provide small s ur-i ace tridge; also toprovide'weightsfor thecartridge so as to locate the center'of gravity'ofthe arm-- and cartridge near'the needle, and yet have low" needlepressure, and a light-weight arm com-'-' pared to the weight of thecartridge, so that the moment .of inertia ofthe arm and=cartridge-,:"later more fully described. I about'itsnhorizontal pivotalsupport,willbe ash The armelements land 2' are e'x'tl'al'idecl"forgreat as possiblefor its total weight and needle wardly beyond the cross member 3 andbent ana vertical' swinging movementabout pins-6 gularly a small amountas indicated at 8 and 9, these extending ends being inserted into holesin the rear end of the cartridge and secured therein by set screws orthe Lke l l or any other suitable fastening means to hold the cartridgesecurely and firmly to the arm elements I and 2.

The translating or needle element 12 preferably consists of a smallplastic moulding having a larger flag portion l3 which is held in thecartridge by any suitable number or screws M, or other suitablefastening means, as seen in Figs. 1 and 2. The smaller extension portionor vibratory arm of this translating element holds the needle pointorstylus i5. The vibratory arm is of insulating material, as polystyrene,and at least one surface has a strain-sensitive coating, as of colloidalgraphite, whereby fiexure of the arm varies the resistance of thecoating and provides the desired electrical variations. Translatingelements of this type are shown, for eX- ample, in Germeshausen Patent2,329,526. The end of this vibratory arm must be free to follow therecord groove, and the vibration of the needle point, and the bend-ng ofthe needle arm, should not be transmitted to the cartridge or any otherpart of the whole tone arm. To accomplish this the cartridge It, thetone arm T and the rotor 1 must provide a sufficient amount of inertiaand stay within the desired low limits of needle pressure. It isdesirable that the center of gravity of the cartridge and arm T shouldbe as near the needle point and as low as possible in position andweight. To facilitate this, weight-elements l6 are provided in thecartridge near its forward end. In the particular arm and cartridgeassembly here being described, the center of gravity of the combinationis slightly forward of the rear end of the cartridge; and it ispreferably not more than one-third of the distance from the needle tothe mounting point in any construction.

The arm T and cartridge must be free to rotate in vertical planes aboutan axis passing through the axis of the fulcrum pins 6- and through thecenter of rotation of the rotor 1, which rotor rotates in a horizontalplane about its vertical axis. This vertical and horizontal movement ofthe arm T must be accomplished freely without any other motion. Therotor I is relatively heavy and has comparatively large mass distributedmore or less similarly to a fly wheel, in order to provide the greatestamount of inertia for the weight actually used. For convenience thefulcrum points between the rear ends of the armelements I and 2 and therotor l are indicated at A and B which points are preferably from two tothree inches apart. This assembly of rotor 1, arm '1 and cartridge Itprovides an amount of inertia in the plane indicated by the points AB!5, which holds the flag l3 of the needle in sufiiclent equilibrium whilethe needle vibrates. The construction of the rotor and the supportingparts later described should be such that the plane ABI5 is eitherparallel to or at a small angle to the surface of the record [1 for thisinertia to be most eifective.

The support for the tone arm comprises the rotor i above referred to,the ball-type thrust bearing it, the stator l9 and the damper having acentral opening 2|. The stator has a central opening 22 screw threadedto receive complemental threads on the lower end of the tubular pivotpin 23 which is rigidly mounted in the stator to project upwardlytherefrom through complemental central openings in the thrust bearingand the rotor, the rotor being rotatably 4 mounted upon tube 23 butwithout any looseness that might allow vibration in the rotor. Thethrust bearing I8 is provided with an annularly arranged series ofopenings 24 receiving the antifriction balls 25. The damper element 20 iof any suitable material to absorb any vibration that might be set up inthe tone arm as a whole and to prevent any vibration being transferredfrom the support to the tone arm.

Longitudinally movable along either one or both of the arm-elements land. 2 is a vibration damper 26 which is a mass of any suitable materialthat can be selectively fastened to the arm-element at any point where avibration position might occur at low frequencies, and the function ofwhich is to interfere with any natural resonant frequency that mightoccur in the arm-elements and to reduce or prevent such vibrations fromoccurring. The arm-element l and 2 are purposely made of thin-walled,small diameter, metal tubing which is grounded. The wires to the needleare placed inside of these tubes which shield them from any outsidemagnetic or electrostatic fields. The small surface area reducespractically to Zero any sounding board effect that might be caused byany forced vibration that might get into arm T from the cartridge. Thesurface of the arm T, the cartridge Ii! and the rotor 1 may be coveredwith some soft material, as a sprayed plastic coating, that willinterfere with the transmission of any vibration to the air.

As will be understood the rotatable record head I! will be driven by anysuitable means within a cabinet or other suitable housing, the surfaceof which is indicated at 21, the support 1, l8, l9 and 20 also restingupon surface 2'! at a point adjacent the edge of the rotating recordholding table H, the record being indicated in dotted lines at 28.

The form of my invention shown in Figs. 4-6 is in general the same asthat shown in Figs. 1-3 except for detailed structural differences. Thesupport for the tone arm consists of the rotor 31, stator 38, and softvibration damping base 39, the rotor 31 being rotatably mounted on thestator 38 by means of a pin 40 threaded into the stator and having atits upper end a head 4| between which head and the bottom surface 42 ofthe depression 43 is mounted a spring 44 to yieldably hold the rotoragainst the stator, the rotor being rotatable about pin 40 with a closerotatable fit in order to prevent any vibration between these parts.Formed on the lower face of the rotor is an annular flange 45 providedwith a flat bottom face to have rotatably sliding movement upon theupper face 46 of the stator so as to decrease the friction between theseparts and enable an easy but vibrationless rotation therebetween. Thisflange 45 should be of substantial diameter for stability, but not solarge as the rotor 37, to minimize frictional resistance.

The tonearm indicated generally at T in Fig.

- 5, comprises the arm-elements 41 and 48 which may be of any desiredsmall cross section, these arms being preferably made of very thin metaltubing through which the wires from the needle extend. The rear end ofthe tone arm is pivotally mounted to the rotor by the fulcrum pins 49,the axis of which when extended intersects the axis of rotation of therotor. The holes in the rear ends of arm elements 41, 48, through whichthe fulcrum pins extend, are of a close rotating fit so as to preventrotation between these parts, the fulcrum pins 49 being threaded intothe rotor and screwed inwardly so asto permit free rotation but preventany looseness" or vibration. The cartridge is rigidly attached to thefront'ends of thearm-elements 41, 48, in the position shown'in Fig. 5,this form of cartridge also having weight elements 50 in the forward endsimilar to the elements It in Fig. 2. The arm-elements ll, 48areconnected together at their respective ends by crossbraces 5| and 52which areheld rigidly but longitudinally adjustably to thesearm-elements by tighteningthe screws 53 and 5 3. Vibrational dampingmaterial will be positioned around the transversecross brace 52 tofunction in a manner similar to that described abovein connectionwiththe vibration damper 26. Cross braces 5i and 52 also contain wood crosssupports a and f {preferably softwood with the grain longitudinally ofthe armfwhich serves well as vibration dampeners and can be shifted tofind an anti-nodal point. Cross braces 51 and 52, as will be understood.also give 'added rigidity to the tone arm T as a whole. Damping materialwill also be positioned around the fulcrum pins 29 to further preventvibration.

The forms of my invention described above give very desirable resilienceand flexibility to the tone arm. It is important to note that the smallsurface area of the arm-elements of my novel tone arm reduces the effectof forced vibration, and that the damping reduces vibration from thecartridge to the arm and allows a slight flexibility which means bettertracking. Also the center of gravity of the arm and cartridgecombination is kept as near the needle point as possible, and myconstruction as described is such that it tends to have as high a momentof inertia about the pivot as is possible with its weight which is keptlow by light weight construction and which in effect causes the motionof the arm and cartridge combination to simulate that of a simplependulum.

The tone arm and cartridge of the present invention is such that theneedle will track better and follow record warping or otherirregularities better and with less needle pressure than any tone armsheretofore known. In the present construction I have made possible avery light needle pressure, for example between A and one ounce, andpreferably in the neighborhood of from to ounce, in connection withwhich it is important to note, as stated above, that the center ofgravity is near the needle and that counterbalancing has been entirelyeliminated. This device will operate eiiiciently at very low needlepressures. I have provided a very solid cartridge that can clamp theneedle rigidly for the best results and vibration of the needle ispermitted without creating undesirable vibrations in the other parts, itbeing noted in Figs. 1 and 2 that suflicient space is provided foraround the needle portion I2, while at the same time firmly clamping theflag l3 in the cartridge and firmly connecting the cartridge to thefront end of the arm-elements.

The cartridge is formed with thin construction in order to reduce itsweight and still maintain its strength, it being noted that the heightof the cartridge has been kept low. The balance point of the arm isquite close to the rear end of the cartridge, and this sets up a highmoment of inertia considering its total weight, to resist any rotationaldisturbances in a horizontal plane which is the direction from whichoutside disturbances would come.

respond simultaneously with the disturbances This inertia effect mustndw li Q ,SQ if hem. ment.o.inertia, .is ,ashigh.

si siblei 'if e irediitheicartridgefmaygibesiip; j

ported fror'n the tubing of the tonjeiarjnif by means.

of ei e j m in'e material to forth Eliminate;

I a flexibility that very materially. increases ,the. life 7, of the 1records;

" The cartridge] should .be;

comparatively fiatQandQnot. t .p. .haviy truer.

tohelp minimize'a twistingtype'of vibration that might occurespeciallyin the cartridge ma ver-" ticalplane"at"rightangles to the line passingthrough the point of theneedleand the center of rotation of the rotor T.Th e extra width betweenthe'pointsAHatthe rear I arm helps reduce theobjectionable vibration just referred to The tone arm.tubingserves as ashield for. the Wires which will run through. it

as stated above and the usei'ofjfsrnall.tubinghelps cause thebulk of theweight toibefi'nithe cart gje. Needle pressures between and one mascarapreferable, the lower values being used when suiiicient tracking on therecord is obtained.

In order to have the greatest possible vibration response in the needleand the least amount in the cartridge and tone arm, the metal needle tipin its plastic mould is made as light as possible and the tone armrelatively heavy. In tone arms prior to the present invention thislatter weight is supplied by a heavy tone arm having a considerableamount of distributed weight, and in some tone arms the arm extends backbeyond the pivotal point so as to carry a counterweight which is ampleto control the needle pressure, while in some instances the arm extendsback beyond the pivoted point so that a variable spring can be attachedto control the needle pressure. The effect of such prior tone arm is tomake the natural motions of the entire arm about a vertical axis in thebase and support similar to that of the compound pendulum and thus slowand sluggish. Such compound pendulum effect also slows any tone armmotions around the horizontal axis in the support. These tone armmotions need to take place to allow the needle to track on warped oreccentric records and to move it as it follows the groove. The tone armof my present invention has no compound pendulum effect but movesquickly and eificiently similar to the motons of a short simple pendulumand this allows it to trace any record irregularity in a much surer andpositive manner.

In order to have the greatest possible vibration in the needle and theleast in the cartridge and tone arm the moment of inertia of theassembly should be as great as possible consistent with its totalweight, needle pressure and necessary design limitation. This relativelylarge moment of inertia is obtained by keeping the weight of the tonearm low and the weight of the cartridge as high as a limited needlepressure will permit. Also the center of percussion should be in thefront end of the moulding that holds the metal needle. The cartridgeshould be kept reasonably small and as compact as possible.

Having thus described my invention, I claim:

A tone arm comprising a light-weight rigid arm having small surfacearea, said rigid arm comprising two spaced tubes of small diameterrigidly held for movement as a unit, a cartridge rigidly carried nearone end of said arm, said end' of the .tone

of to locate the center of gravity of the arm and cartridge nearer thecartridge than the other end of the arm, a support of relatively largemass compared to the mass of the rigid arm comprising a rotor and astator, the rotor being rotatable on the stator in a horizontal plane,and means for mounting the other end of said tubes on opposite sides ofsaid rotor for rotation therewith in the same direction and for pivotalmovement in vertical planes, the points of pivotal mounting on oppositesides of said rotor being spaced substantially farther apart than thewidth of said cartridge.

ROBERT S. JOHN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Number Name Date Theis Mar. 1, 1921 CheneyNov. 27, 1923 McClatchie Nov. 10, 1931 Forte Apr. 2, 1935 Proctor Nov.10, 1936 Thompson Oct. 18, 1938 Hutter Apr. 1, 1941 Vermeulen Jan. 19,1943 Dally Mar. 9, 1943 Andres Aug. 10, 1943 Germeshausen Sept. 14, 1943Jones Oct. 5, 1943 FOREIGN PATENTS Country Date Great Britain Oct. 27,1927 Great Britain Dec. 12, 1929 Great Britain Apr. 17, 1930 France July31, 1933 Great Britain Oct. 22, 1934

